BrainstemMedulla

David A. Morton, Ph.D.Jan 17th, 2013

Objectives• Describe the trajectory of the cranial nerves, their components, and their functions• Identify and locate the CN’s associated with the medulla, the pons and the

midbrain.• Explain how cranial nerves differ from spinal nerves• List the cranial nerves that contain parasympathetic fibers, the location of their

nuclei, and their function• Recognize the major internal and external landmarks on the dorsal and ventral

surface of the brain stem, so that you can determine if a gross or stained cross section is medulla, pons or midbrain.

• Identify on a typical cross section all the brain stem nuclei containing motor neurons that end on striated muscle.

• Explain why cranial nerves are so important in localizing lesions.• Name reflexes that test these nerves and brain stem levels.• Relate branches of the vertebrobasilar blood supply to the medulla and pons

explaining the deficits that would occur with vascular occlusion.

Internal anatomy of brainstem

Alar

Basal

Sulcus limitans

Spinal cord

Som S

VS

VM

SM

Alar

Basal

Sulcus limitans

Medulla

Som S

VSVM

SMBM

The fate of the alar and basal laminae

• Why are brain stem sensory nuclei lateral

to motor nuclei in brainstem?

External anatomy:

• Pyramid

• Olive

• CNN VIII, IX, X, XI and XII

• Fourth ventricle

• Vertebral arteries

Medulla oblongata

IX & XXII

XI

VIII

Medulla

4 th vent.

O P

Horizontal section

O

P

Alar

Basal

Medulla

Som SVS

VMSM

BM

Sulcus limitans

Solitary nuclei and tract Spinal

trigeminal

nucleus

Hypoglossal

nucleus

Inf sal and dorsal vagal nuclei

Nucleus ambiguus

Medulla oblongata

Medulla Oblongata

Hypoglossal nucleus (CN XII)

• Somatic motor

• Comparable to ventral horn

• Tongue muscles

Medulla Oblongata

Dorsal motor nucleus (CN X)

• Visceral motor

• Comparable to lateral horn

• Origin of preganglionic

parasympathetic neurons

Medulla Oblongata

Inferior salivatory nucleus (CN IX)

• Visceral motor

• Comparable to lateral horn (can

not see it on brains)

• Origin of preganglionic

parasympathetic neurons to otic

ganglion

Medulla Oblongata

Nucleus ambiguus (CN IX and X)

• Branchial (spec visc) motor

• Origin of BM neurons for IX and X

Medulla Oblongata

Reticular formation

• Forms the central core of brain stem

• Nuclear groups not obvious

Medulla Oblongata

Vascular supply:

• Vertebra artery

• Anterior spinal artery

• PICAPICA

Ant sp

Vert

Objectives

• Explain what the meninges cover and what spaces they surround.• For each meningeal space describe a classic source for blood in the space.• Describe where CSF is produced and how it circulates and is removed.• Name the most likely sites of obstruction of CSF circulation and the

consequences.• Explain how the Blood Brain Barrier is different from the CSF Brain interface.

Cranial Meninges Dura materArachnoid materPia mater

Cranial Meninges

Cere

bral

vv.

Dural Venous sinuses

Dura mater (2 layers in the skull)• Periosteal layer and Meningeal layer

• Dural venous sinus

Meningeal hemorrhages

Blood in meningeal spaces or potential spaces

1. Epidural hemorrhage

2. Subdural hemorrhage

3. Subarachnoid hemorrhage

Epidural space

Dura mater• Middle meningeal artery

Epidural hemorrhageTorn middle meningeal a.

Epidural hemorrhage

Subdural space

Dura mater• Bridging cerebral vein• Courses between cerebrum and

dural venous sinus

Subdural hemorrhage Torn bridging cerebral v.

Dural Venous sinuses

What space is the artery located?

Brain arteries – Subarachnoid space

Internal carotid artery (ICA)

• Ophthalmic

• Anterior cerebral

• Middle cerebral

Vertebral artery

• PICA

• Basilar

• AICA

• SCA

• Posterior cerebral

Cerebral arterial circle of Willis

• Anterior communicating

• Anterior cerebral

• ICA

• Posterior communicating

• Posterior cerebral

Subarachnoid hemorrhage

Stroke

Subarachnoid space

Lateral ventricle

Lateral ventricle

Interventricular foramen

Foramen of Monro

3rd ventricle

Cerebral aqueduct

Aqueduct of Sylvius

Mesencephalic aqueduct

4th ventricle

Lateral apertures

Foramen of Luschka

Median apertureForamen of Magendie

Arachnoid granulationsSuperior sagittal sinus

Choroid plexus

Organize the following terms:

Subarachnoid space

Lateral ventricleLateral ventricle

Interventricular foramen Foramen of Monro

3rd ventricle

Cerebral aqueduct Aqueduct of Sylvius Mesencephalic aqueduct

4th ventricle

Lateral apertures

Foramen of Luschka

Median aperture

Foramen of Magendie

Arachnoid granulations

Superior sagittal sinus

Choroid plexus

The following terms are in order:

The ventricular systemThe ventricles, lined by ependymal cells, are obvious internal landmarks, and are important as internal structures to relate other structures to. Try to visualize them and rotate them with the brain. They will form the “wire frame” for our orientation to the brain.

The ventricular system

The ventricular system

Hydrocephalus is dilation of all or part of the ventricular system due to

obstruction of CSF flow. There are two types:

1. Obstructive (non-communicating) hydrocephalus. Block in the ventricular

system or the outlet foramina.

2. Communicating (non-obstructive) hydrocephalus. Block in the subarachnoid

space or the arachnoid granulations.

a. Meningitis followed by scarring.

b. Subarachnoid hemorrhage, meningeal fibrosis and scarring

Copyright © 2010 Pearson Education, Inc.

Copyright © 2010 Pearson Education, Inc.

Hydrocephaly

1. Obstructive (non-communicating) hydrocephalus. Block in the ventricular system or the outlet foramina.

Copyright © 2010 Pearson Education, Inc.

Hydrocephaly2. Communicating (non-

obstructive) hydrocephalus. Block in the subarachnoid space

or the arachnoid granulations.

Copyright © 2010 Pearson Education, Inc.

Figure 12.26a Formation, location, and circulation of CSF.

Superiorsagittal sinus

Arachnoid villus

Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura mater

Right lateral ventricle(deep to cut)

Choroid plexusof fourth ventricle

Central canalof spinal cord

Choroidplexus Interventricularforamen

Third ventricle

Cerebral aqueductLateral apertureFourth ventricleMedian aperture

(a) CSF circulation

CSF is produced by thechoroid plexus of eachventricle.

1

CSF flows through theventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord.

2

CSF flows through thesubarachnoid space.

3

CSF is absorbed into the dural venoussinuses via the arachnoid villi.

4

1

2

3

4